A light emitting diode (LED) is mainly formed by light emitting semiconductor material multi-epitaxy. Take a blue light LED for example. A blue light LED is manly formed by GaN-based epitaxial films, and a main structure includes a sandwiched light emitting body stacked from an N-type semiconductor layer, a light emitting layer, and a P-type semiconductor layer. LEDs, based on their structures, are categorized into horizontal, vertical and flip-chip types, with a main structure including an N-type semiconductor layer, a light emitting layer and a P-type semiconductor layer. An LED is capable of converting electric energy to light. In order to input electric energy to the light emitting body of an LED, two electrode structures, respectively electrically connected to the N-type semiconductor layer and the P-type semiconductor layer, need to be provided on the light emitting body.
FIG. 1 shows an electrode structure of a conventional LED, which mainly includes an adhesion layer 1 and a bond pad layer 2. The adhesion layer 1 includes a chromium layer 1A (18 angstroms (Å)), a first metal layer 1B (2500 Å) and a second metal layer 1C (500 Å). The bond pad layer 2 includes a platinum layer 2A (400 Å) and a gold layer 2B (18000 Å). The bond pad layer 2 serves for wire bonding purposes, and its gold layer 2B needs to have a thickness of 18000 Å in order to satisfy requirements of adequate wire bonding hardness and reduced electromigration. It is apparent that the amount of gold used is quite large. One reason for such is that, aluminum has inadequate hardness that cannot be readily used for wire bonding and produces electromigration under large-current operations. However, as the cost of gold is far greater than that of aluminum, production costs resulted are high.
Given that optoelectronic characteristics of an LED are not affected (or similar effects are achieved), in order to reduce production costs, one current development trend is replacing gold by other materials. For example, the Taiwan Patent No. I497767, replaces aluminum by an aluminum alloy to solve the electromigration produced under large-current operations. However, characteristics of an aluminum alloy are still quite similar to those of aluminum; that is, the hardness requirement for wire bonding is not exactly satisfied, nor is the issue of electromigration reliably solved.